Effect of electrode material on contact high-voltage polarization in a vinylidene fluoride-hexafluoropropylene copolymer |
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Authors: | V V Kochervinskii E V Chubunova Yu Yu Lebedinskii N A Shmakova |
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Institution: | 1.Karpov Institute of Physical Chemistry,Moscow,Russia;2.Moscow Engineering Physics Institute (National Nuclear Research University),Moscow,Russia |
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Abstract: | High-voltage polarization processes occurring in alternating fields of various frequencies in extruded films of vinylidene
fluoride-hexafluoropropylene copolymers are studied. Remanent polarization typical for ferroelectric polymers with a polar
cell appears during crystallization in the nonpolar α phase. This effect is associated with the presence of a highly imperfect
ferroelectric (or antiferroelectric) phase in the copolymer, where chains assume planar zigzag conformations. The magnitude
of remanent polarization depends on the frequency of the applied bipolar sawtooth voltage. This observation may be explained
by the fact that the resulting field is created not only by the external source but also by the space charge that is contributed
by carriers injected from electrodes. With the use of deposited Au and Al, the role of electrode material in polarization
and conduction processes is ascertained. In the case of Al, Al2O3 and new Al-C chemical bonds are formed on the polymer surface. Owing to formation of these additional dielectric layers at
the copolymer/metal interface, electrodes may be blocked partially. The above new chemical bonds facilitate formation of deeper
surface traps for carriers; as a result, the remanent surface potential appears in polarized samples even after storage in
the short-circuit mode. |
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